Commercial-grade explosives discovered on the ocean floor south of Los Angeles prompted authorities to ban cell phone use Wednesday to prevent accidental detonation.

Environmental divers hired to check on algae growth in the Huntington Beach Harbour found the cigarette-sized blasting caps late Tuesday.

At least eight of the volatile explosives, which often are used to trigger larger explosions, were intentionally placed beneath nine to 15 feet of water near the shore, said Jim Amormino, spokesman for the Orange County Sheriff’s Department.

Given how little detail is provided, how, exactly, do authorities know that terrorism isn’t involved?